Endocrine Abstracts

Objective: To evaluate the success of administration of ¹³¹Iodine adjusted for thyroid gland size in the treatment of hyperthyroidism in Graves’ disease.

Methods: All patients with Gravés hyperthyroidism who underwent therapeutic administration of ¹³¹I in a referral center in Portugal, from 2014 to 2022 were selected. Values of estimated thyroid gland size, administrated doses of ¹³¹I and 24h radioactive iodine uptake (RAIU) prior to therapy were collected. Thyroid function was evaluated 3, 6 and 12 months after administration. The goal of RAI treatment was to achieve eu- or hypothyroidism within 12 months.

Results: This study included 135 ¹³¹I administrations in a total of 130 patients (84% female, mean age 47 years) with a mean time since diagnosis of 63 years. 132 patients (98%) had been previously treated with antithyroid medications (86% with methimazole and 12% with propylthiouracil) and 4 underwent more than one RAI treatment. The mean estimated thyroid gland size was 57.7g, range 14-172g. Mean RAIU was 54.1%, range 19-75%, with RAI administrated doses ranging from 4 to 23mCi, with a mean dose of 11.4mCi. Three months after ¹³¹I administration, hyperthyroidism was documented in 47 patients (38%), euthyroidism in 38 (30%) and hypothyroidism in 40 (32%). At 6 months, 7% of the individuals who had hyperthyroidism at 3 months recovered, with a total of 40 patients with hyperthyroidism. Also, by this time, 20 patients (16%) had euthyroidism and 68 (53%) were hypothyroid. Twelve months later, the decreasing tendency of hyperthyroidism was maintained, with a total of 35 (28%) patients remaining hyperthyroid. Additionally, 14 individuals (11%) had euthyroidism and 75 (61%) were hypothyroid.

Conclusion: The overall Graves’ disease treatment success rate obtained with ¹³¹I administration adjusted for thyroid gland size at our institution was 72%, similar to previous studies.